Ok, I pull the recoil spring out of a gun with supposedly less than 100 rounds and put in a new one.
I fire 30 rounds and pull the spring to measure and compare and here is what I found.
Brand new spring - 1.55 in
used - < 100 rds - 1.284 in
( I think much more)
w/ 30 rds - 1.257 in
Now that 30 round spring lost almost 1/3 of an inch. From previous posts in the past, some guys would freak out at that loss and replace it.
I'm sure someone smarter than me will chime in, but I sticking to my original story that it is not all about length, but compression as well.
Who knows, maybe those springs do a rapid compress after the first mag, then slowly compress afterwards.